What is Equine motor neuron disease?

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Equine motor neuron disease (EMND) is a relatively new condition that affects the nervous and muscular systems in adult horses.Equine motor neuron disease (EMND) is a relatively new condition that affects the nervous and muscular systems in adult horses.

It was first diagnosed in the US in 1990 in New York state,  and has also been diagnosed as far west as the state of Oregon.

It is most prevalent in the US, and to date, fewer than 200 horses have been diagnosed with EMND.

Affected horses demonstrate marked weight loss in the face of a ravenous appetite. This weight loss is attributed to neurogenic muscular atrophy. Presently there is no know cause of the disease.

A horse with this condition appears with muscle tremors, and may appear to be “tied up,” (short-strided gait). Other signs may include constant shifting of weight in the rear limbs and abnormally low head carriage. The horse also has a particular stance, with all four limbs camped (tucked) under.

The condition usually progresses with continued muscle atrophy and debilitation over the course of one to several months. Occasionally the condition will stabilize or even seem to improve one to two months after the onset. Following this period in many horses, the condition becomes progressive, requiring euthanasia.

A few horses have stabilized for as long as three years, however, none have returned to effective use.

The horse characteristically has mild elevations of the muscle-derived enzymes, CPK and AST. Electromyography (EMG) is frequently used as an aid in the diagnosis of this condition. Although there is no definitive diagnostic test available for this condition, the clinical signs, changes in muscle enzymes and EMG findings provide strong support for the diagnosis of EMND. Muscle and nerve biopsies have characteristic findings of EMND.

A definitive cause for EMND has not been determined; a common toxin has not been identified and infectious agents are not likely because of the sporadic nature of the disease. Horses without access to pasture seem to be at higher risk for developing the disease.

Although speculative, it is suggested that some oxidative injury may cause the neuronal cell death leading to the clinical signs. Vitamin E is a dietary antioxidant which may be useful in halting the progression of the disease.

Clinical signs

Active phase
Trembling – muscle tremors and fasciculations.
Excessive periods of recumbency.
Abnormal limb positioning – weight onto rear legs and hold all 4 limbs closer together than normal.
Weakness without ataxia.
Appetite remains normal – normal gut motility.
Malabsorption of nutrients from the gut suggests that absorptive function of the gut is abnormal → abnormal function.
Symmetrical muscle atrophy, especially in triceps , scapula, quadriceps, lumbar , sacral and neck muscles.
Stabilization in 2-8 weeks to arrested form.
Symmetrical buckling of forelimbs while standing.
Abnormally low head carriage.
Sweating.
Elevation of tailhead.
Cranial nerve deficits.
Persistent recumbency, respiratory distress.

Arrested phase
Failure to gain weight despite normal appetite.
Exercise intolerance.
Excessive recumbency.
Tailhead elevation.
Abnormal gait – stumbling, stringhalt-like in several limbs.

 

This article reprinted with permission from Horseadvice.com, an internet information resource for the equestrian and horse industry since 1994. On the WWW at www.horseadvice.com we have tens of thousands of documents on the web about horse care, diseases, and training.

 

Clinical signs information from Vetstream

 

2 thoughts on “What is Equine motor neuron disease?

  • February 14, 2014 at 8:56 am
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    I recently noticed on my 4 yr old Paint Gelding he has lost all the muscle on his cheeks to his eyes, his head looks like it is very narrow, he is 16.1hh and in good condition, he is not showing any of the other signs mentioned in your notes. Do you think this is the start of Motor Neuron Disease. Can a blood test tell me what the problem is? Thankyou Meredith Rehn

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  • July 7, 2015 at 9:23 am
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    In May of 2014 my horse randomly came up lame. For months she was lame. Then she began do loose weight and develop tremors, so we decided I do a blood test to see what she had. The results came back positive for EPM. Though, we were skeptical because she didn’t show symptoms for it. We gave her antibiotics and she showed improvement but because of lack of money we had to stop treating her. For a while she was alright, but it began to get worse again. At the same time, she started shifting her back end. I searched online and didn’t see those as symptoms, but I had no idea what else it could be. It’s been more than a year now and she’s been pretty much the same. A few weeks ago a new vet came and just took a quick look at her for us and right away she knew it was this disease. Now looking at the symptoms, this fits exactly. So, do lots of research and get many opinions from different vets. Tell all of your horsey friends and family about it and tell them to pass it on. Spread the word to help owners know to help treatment of symptoms come quickly and easily. This was a horrible experience and I would never want anybody do have to experience this.

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